Manufacture of semiconductor device with stress structure

ABSTRACT

A method for manufacturing a semiconductor device includes the steps of (a) forming a gate electrode on a silicon substrate, through a gate insulating film; (b) forming a lamination of an insulating film and a sacrificial film having different etching characteristics on the silicon substrate, covering the gate electrode, and anisotropically etching the lamination to form side wall spacers on side walls of the gate electrode and the gate insulating film; (c) implanting impurities into the silicon substrate on both sides of the side wall spacers; (d) etching the silicon substrate and the sacrificial film to form recesses in the silicon substrate, and to change a cross sectional shape of each of the side wall spacers to approximately an L-shape; (e) epitaxially growing Si—Ge-containing crystal in the recesses; and (f) depositing an insulating film containing stress, covering the side wall spacers.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 12/606,720, filed on Oct. 27, 2009, which is a continuationapplication of PCT/JP2007/000514, filed on May 14, 2007, the entirecontents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a semiconductor devicemanufacture method.

BACKGROUND

MOS transistor has been developed along the basic principle that “it ispossible to realize high speed through miniaturization” according to ascaling rule. However, as the result of progress of excessiveminiaturization, it is necessary to increase amount of impurities to bedoped in a channel region in order to suppress rapid reduction in thethreshold voltage to be caused by miniaturization. Because of “impurity”scattering, mobility of carriers (electrons, holes) transporting fromthe source to drain reduces greatly. In order to suppress this mobilityreduction, various countermeasures have been adopted for forciblyapplying “strain” to a silicon atom group constituting the channel.

Electron mobility in an n-channel (N) MOS transistor is improved byapplying tensile stress to the channel. Hole mobility in a p-channel (P)MOS transistor is improved by applying compressive stress to thechannel.

Japanese Patent Laid-open Publication No. 2003-86708 and its family US2004/0075148, the whole contents of which are incorporated herein byreference, disclose that in case where the gate length direction isdisposed along a <110> direction on an Si (001) surface, NMOS increasesan on-current upon application of tensile strain along the gate lengthdirection, and increases an on-current upon application of tensilestrain along the gate width direction, whereas PMOS reduces anon-current upon application of tensile strain along the gate lengthdirection (increases an on-current upon application of compressivestrain along the gate length direction), and increases an on-currentupon application of tensile strain along the gate width direction. Thesedocuments further disclose that by forming the contact etch stopper filmwith a tensile stress film above the NMOS region and forming the contactetch stopper film with a compressive stress film above the PMOS region,the whole characteristics of CMOS can be improved and stress can beadjusted by an area of the contact etch stopper film.

Japanese Patent Laid-open Publication No. 2003-273240 and its family US2003/0181005, the whole contents of which are incorporated herein byreference, disclose that in the state that the semiconductor surfacebetween the gate electrode and the isolation region is covered with aninsulating film functioning as a contact etch stopper, a tensile stressfilm is formed above the NMOS region and a compressive stress film isformed above the PMOS region.

Japanese Patent Laid-open Publication No. 2006-13322 and its family US2005/0285137, the whole contents of which are incorporated herein byreference, analyses stresses in various directions and the performancesof NMOS and PMOS formed in a silicon substrate comprehensively andproposes to release the stress of a compressive stress film formed onPMOS on the isolation region.

It is also possible to apply stress to a channel by means other than theetch stopper.

When the source/drain regions of an NMOS transistor are made ofsilicon-carbon (Si—C) mixed crystal (C-doped Si) having a latticeconstant smaller than the Si substrate, tensile stress is applied to theSi crystal in the channel region and electron mobility becomes high.Refer to K. Ang et al.: IEDM Tech. Dig., 2004, p. 1069, the wholecontents of which are incorporated herein by reference.

When the source/drain regions of a PMOS transistor are made ofsilicon-germanium (Si—Ge) mixed crystal having a lattice constant largerthan the Si substrate, compressive stress is applied to the Si crystalin the channel region and hole mobility becomes high. Refer to T. Ghaniet al.: IEDM Tech. Dig., 2003, p. 978 and Y. S. Kim et al.: Proceedingsof ESSDERC 2005, p. 305, the whole contents of which are incorporatedherein by reference.

By applying stress to the channel of a MOS transistor, it becomespossible to increase carrier mobility and improve the performance of theMOS transistor. Electron mobility in an NMOS transistor is increased bytensile stress, and hole mobility in a PMOS transistor is increased bycompressive stress.

It is possible to apply desired stresses to PMOS and NMOS transistors,by etching and digging the source/drain regions of a PMOS transistor andgrowing Si—Ge crystal and by etching and forming the recess in thesource/drain regions of an NMOS transistor and growing Si—C crystal.However, in this case, manufacture processes become complicated. Moresimple manufacturing processes are desired.

Thus, studies are being made on the structure in which the source/drainregions of a PMOS transistor are etched to form recesses, Si—Ge (orSi—Ge—C) crystal is grown in the recesses to apply compressive stress tothe channel, after forming a silicide layer, a nitride film havingtensile stress is deposited on the NMOS transistor to apply tensilestress to the channel of a NMOS transistor.

A complementary type semiconductor device may be formed through buryingcrystal having a larger lattice constant than silicon in thesource/drain regions of PMOS, forming a compression stress film on PMOS,and forming a tensile stress film on NMOS. It is desired to improve theperformance of the semiconductor device of this type and stabilize themanufacturing processes.

SUMMARY

According to an aspect of the embodiments, a method for manufacturing asemiconductor device includes:

(a) forming a gate electrode on a silicon substrate, through a gateinsulating film;

(b) forming a lamination of an insulating film and a sacrificial filmhaving different etching characteristics on the silicon substrate,covering said gate electrode, and anisotropically etching the laminationto form side wall spacers on side walls of the gate electrode and thegate insulating film;

(c) implanting impurities into the silicon substrate on both sides ofthe side wall spacers;

(d) etching the silicon substrate and a portion of the lamination of theside wall spacers to form recesses in the silicon substrate and change across sectional shape of each of the side wall spacers to approximatelyan L-shape;

(e) epitaxially growing Si—Ge-containing crystal in the recesses; and

(f) depositing an insulating film containing stress, covering the sidewall spacers.

According to another aspect of the embodiments, a method formanufacturing a complementary type semiconductor device includes:

(a) forming gate electrodes in a PMOS region and an NMOS region on asilicon substrate, through a gate insulating film;

(b) forming an insulating layer including a silicon nitride film and asilicon oxide film formed thereon on the silicon substrate, covering thegate electrodes, and further forming a sacrificial layer on theinsulating layer;

(c) anisotropically etching the sacrificial film to leave thesacrificial film only on side walls of the gate electrode in a side wallspacer shape;

(d) covering the NMOS region with a mask, further anisotropicallyetching the insulating film to pattern the insulating layer by using thesacrificial film as an etching mask to expose silicon surface in thePMOS region;

(e) removing the mask covering the NMOS region, etching regions of thesilicon substrate with exposed silicon surface in the PMOS region toform recesses, and removing the sacrificial film while leaving thesilicon oxide film which has been covered with the sacrificial film;

(f) epitaxially growing Si—Ge-containing crystal in the recesses;

(g) anisotropically etching the silicon nitride film not covered withthe silicon oxide film in the NMOS region;

(h) forming a silicon nitride film having tensile stress above the NMOSregion; and

(i) forming a silicon nitride film having compressive stress above thePMOS region.

The insulating film for applying stress to strain the channel is desiredto be formed at a position as near to the channel as possible. Since thesacrificial film is removed at the same time when the recesses areformed, the processes are simple and the strain applying structure canbe obtained stably.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1O are cross sectional views of a semiconductor substrateillustrating main processes of a method for manufacturing acomplementary type semiconductor device according to a first embodiment;

FIGS. 2A to 2D are cross sectional views of a semiconductor substrateillustrating main processes of a method for manufacturing acomplementary type semiconductor device according to a secondembodiment;

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described with reference tothe accompanying drawings.

Description will be made on main processes of a method for manufacturinga semiconductor device according to the first embodiment with referenceto FIGS. 1A to 1O.

First, an isolation region is formed in a surface layer of a siliconsubstrate to define a plurality of active regions.

As illustrated in FIG. 1A, a silicon oxide (abbreviated to SiO in somecases) film 2 a having a thickness of about 10 nm is formed, forexample, by dry thermal oxidation at 900° C., and then a silicon nitride(abbreviated to SiN in some cases) film 2 b having a thickness of about110 nm is deposited by chemical vapor deposition (CVD) at 750° C. usingSiH₂Cl₂/NH₃.

A photoresist pattern having an opening corresponding to the isolationregion is formed by photolithography, the silicon nitride film exposedin the opening is etched, and a trench T having a depth of about 300 nmis formed in the surface layer of the silicon substrate, by using thepatterned silicon nitride film as a hard mask. Etching gas may be CF₄for SiN, CF₄/N₂ mixed gas for SiO, and CF₄/O₂/N₂ for Si, etc.

Insulator, e.g., a silicon oxide film formed by high density (HD) plasmaenhanced (PE-) CVD, is deposited on the substrate to bury the trench T.An unnecessary silicon oxide film on the silicon nitride film 2 b ispolished and removed by chemical mechanical polishing (CMP) to form theembedded isolation structure. In this manner, an isolation region 3(FIG. 1B) is formed by shallow trench isolation (STI). The siliconnitride film 2 b on each active region defined by the isolation regionis removed by a wet process, e.g., with phosphoric acid heated to 150°C. The exposed oxide film 2 a is removed with hydrofluoric acid.

As illustrated in FIG. 1B, p-type impurities, e.g., B ions, and n-typeimpurities, e.g., P ions, are selectively implanted by using resistpatterns to form a p-type well PW and an n-type well NR. The p-type wellPW constitutes an NMOS region for forming an NMOS transistor, and then-type well NW constitutes a PMOS region for forming a PMOS transistor.The p-type well and n-type well are collectively called active region(s)in some cases.

As illustrated in FIG. 1C, a thermally oxidized film 4 having athickness of about 1.5 nm is formed, for example, by dry oxidation.Thereafter, a polysilicon layer 5 is deposited, for example, to athickness of about 100 nm by CVD at a temperature of about 600° C.Impurity ions are doped in the polysilicon layer 5 by using resistmasks. In the NMOS region, phosphorus P ions are implanted, e.g., at8×10¹⁵ cm⁻², and in the PMOS region, boron B ions are implanted, e.g.,at 6×10¹⁵ cm⁻². Implanted impurity ions are activated by rapid thermalannealing (RTA), e.g., at 1000° C. for about 10 seconds.

After activation, photoresist patterns PR1 of a gate electrode shape areformed on the polysilicon layer 2 b, and the polysilicon layer ispatterned by etching to form gate electrodes 5. Thereafter, thephotoresist patterns PR1 are removed. If a gate electrode having a shortgate length is to be patterned, it is preferable to use a hard mask.

As alternatively illustrated in FIG. 1CX, after impurity ions areimplanted into the polysilicon layer 5 and activated, a hard mask layerHM such as a silicon oxide film is deposited on the polysilicon layer 5by low temperature CVD. Photoresist patterns PR1 are formed on the hardmask layer HM, and the hard mask layer HM is etched by using thephotoresist patterns PR1 as a mask. Thereafter, the photoresist patternsPR1 are removed. The patterns of the hard mask layer HM are trimmed ifnecessary, and the polysilicon layer 5 is etched by using the hard masklayer patterns as a mask. By using the hard mask layer, it becomespossible to pattern reliably a finer gate electrode. The patterns of thehard mask layer HM may be left without being removed.

Reverting to FIG. 1C, by selecting the NMOS region and PMOS region byusing resist masks, impurity ions are implanted into the NMOS region andPMOS region to form extensions of sources/drains and pockets. Withrespect to the NMOS region, ions, e.g., As ions, are implanted into thep-type well PW at an acceleration energy of 3 keV and a dose of 1×10¹⁵cm⁻² (represented by a symbol like 1E15) to form n-type extensions Exn,and ions, e.g., B ions, are implanted at an acceleration energy of 10keV to 15 keV and a dose of 2×10¹³ cm⁻²(2E13) to 4×10¹³ cm⁻²(4E13) alongsymmetric four directions slanted from the substrate normal to formp-type pocket regions Pkp surrounding the n-type extensions Exn.

With respect to the PMOS region, ions, e.g., B ions, are implanted intothe n-type well NW at an acceleration energy of 0.5 keV and a dose of1×10¹⁵ cm⁻² (1E15) to form p-type extensions Exp, and ions, e.g., Asions, are implanted at an acceleration energy of 30 keV to 60 keV and adose of 1E13 to 3E13 along symmetric four directions slanted from thesubstrate normal to form n-type pocket regions Pkn surrounding thep-type extensions Exp. Since the pocket region has the same conductivitytype as the well, the pocket region will be omitted in the followingdrawings.

As illustrated in FIGS. 1D and 1E, a lamination for forming side wallspacers is deposited covering the gate electrode. FIG. 1E is a partiallyenlarged view of FIG. 1D. In order to narrow a gate pitch, the side wallspacer is preferably made thin. In order to suppress the short channeleffects, the deep diffusion regions (source/drain regions) arepreferably spaced from the gate electrode by some distance. When anepitaxial crystal having a lattice constant larger than Si is buried ina recess, it is not preferable that the hetero interface of theepitaxial layer forms a pn junction. The hetero pn junction may causeleak current thereacross. It is preferable to form a diffusion layer ofthe same conductivity type covering the epitaxial layer. A structureusing side wall spacers of an L-shape satisfies these requirements.

First, by CVD at about 500° C. to 600° C., a silicon oxide film 6 isdeposited on the silicon substrate to a thickness of about 3 nm, then asilicon nitride film 7 is deposited to a thickness of about 10 nm to 15nm, and a silicon oxide film 8 is deposited to a thickness of about 6nm, in this order. In this manner, an insulating lamination of athree-layer structure is formed by CVD. Source gases may be SiH₂Cl₂ andN₂O for silicon oxide, and SiH₂Cl₂ and NH₃ for silicon nitride, etc.

It is sufficient if the silicon oxide film 6 provides a function of abuffer layer, and a thickness thereof is preferably 3 nm or thinner. Itis also possible to omit the silicon oxide film 6. It is preferable thatthe silicon nitride film 7 functions sufficiently as an etch stopper andhas tensile stress. A thickness of the silicon nitride film 7 ispreferably 10 nm or thicker. It is sufficient if the silicon oxide film8 provides a function of an etch stopper while a sacrificial layerformed thereon is etched, and a thickness thereof may be 2 nm orthinner.

An amorphous silicon (a-Si) film 9 having a thickness of 10 nm to 15 nmis deposited on the insulating lamination of three layers of the siliconoxide film/silicon nitride film/silicon oxide film, by pyrolysis CVDusing SiH₄/H₂ gas preferably at a substrate temperature of 500° C. orlower. Although a polysilicon (poly Si) film may be deposited by CVD ata temperature of 550° C. or higher, a lower deposition temperature isdesired in order to suppress re-diffusion of impurity distribution. Atotal thickness of the insulating lamination and sacrificial film is setto a thickness suitable for forming the side wall spacer to be used whena deep diffusion layer is formed.

As illustrated in FIG. 1F, by using the silicon oxide film 8 as an etchstopper, the amorphous silicon film 9 is etched by anisotropic dryetching using HBr, to leave the amorphous silicon film only on the sidewalls of the gate electrode structure in a side wall spacer shape.

As illustrated in FIG. 1G, the NMOS region is covered with a photoresistpattern PR2 in the state in which the amorphous silicon film 9 waschanged to the side wall spacer shape, and the silicon oxide film 8,silicon nitride film 7 and silicon oxide film 6 are still not etched. Inthe PMOS region, by using the amorphous silicon film 9 as an etchingmask, the silicon oxide film 8, silicon nitride film 7 and silicon oxidefilm 6 are anisotropically dry-etched. Etching gas may be CF₄/N₂ mixedgas for SiO, and CF₄ for SiN, etc.

In the PMOS region, the silicon oxide film 8, silicon nitride film 7 andsilicon oxide film 6 in an area not covered with the amorphous siliconfilm 9 are etched, and the side wall spacers are left. The surface ofthe silicon substrate is exposed in the PMOS region outside the sidewall spacers. If the patterns of the hard mask layer HM illustrated inFIG. 1CX are left, the gate electrode 5 is covered with the pattern ofthe hard mask layer HM. If the hard mask layer HM is not used, the gateelectrode 5 is also exposed.

In this state, B ions are implanted into the PMOS region, for example,at an acceleration energy of 40 keV and a dose of 1E13 to form a p-typeenvelope region Evp. The p-type envelope region Evp is implanted in theregion outside the side wall spacers, which include the lamination ofthe insulating films 6, 7 and 8 and the sacrificial film 9, formed onthe side walls of the gate electrode 5. The envelope region Evp alsodistributes on the gate electrode side by a distance corresponding tospreading of the ion implantation. Thereafter, the photoresist patternPR2 is removed.

In the p-type envelope region Evp, recess is formed and epitaxial growthis performed in later processes. Therefore, the epitaxial region isenclosed within the p-type envelope region Evp, and a hetero interfaceis formed inside the pn junction front. The epitaxial regions andenvelope regions are collectively called source/drain regions in somecases.

As illustrated in FIGS. 1H and 1I, chemical dry etching is performed forthe silicon substrate. FIG. 1I is a partially enlarged view of FIG. 1H.The silicon substrate in the NMOS region is covered with the insulatinglamination 6, 7 and 8. In the PMOS region, the surface of the siliconsubstrate is exposed in an area outside the side wall spacers. Thesurface of the Si substrate is subjected to chemical dry etching usingCF₄/O₂ as etchant gas. For example, a pressure is 50 Pa and anapplicator power is 100 W.

This chemical dry etching digs the silicon surface exposed in the PMOSregion to a depth of about 50 nm to form recesses 10 in which Si—Gemixed crystal is to be epitaxially grown. This chemical dry etching notonly etches the substrate silicon but also etches the amorphous siliconfilms 9 on the side walls of the gate electrode at the same time. Thesilicon oxide film 8 in the NMOS region not covered with the amorphoussilicon film is also etched. The silicon nitride film 7 is not etched.The silicon oxide film 8 under the amorphous silicon film 9 is left byutilizing an end point monitor by oxygen. At this time, the amorphoussilicon films 9 on the side walls are perfectly removed.

Since the amorphous silicon films 9 of side wall spacers are removed,the side wall spacer on the side wall of the gate electrode becomesthin. The bottom wall of the three-layer lamination structure projectslaterally by a distance corresponding to the thickness of the amorphoussilicon film 9. A projection length is approximately 7 nm or longer. Theside walls of the gate electrode retain the insulated state by theinsulating lamination of the silicon oxide film 8, silicon nitride film7 and silicon oxide film 6.

Thereafter, an HF process is executed slightly as a preparatory processfor epitaxial growth to remove a thin (natural) oxide film on thesilicon surface. A wet etching amount is adjusted to leave the siliconoxide film 8.

As illustrated in FIG. 13, selective epitaxial growth of a B-doped Si—Gelayer 11 is performed by using a gas system of HCl/B₂H₆/SiH₄/GeH₄/H₂,for example, at a substrate temperature of 600° C. A thickness of thegrown film is about 60 nm. Since HCl removes fine nuclei on theinsulating film, crystal growth does not occur on the insulating film.The recess 10 is filled with p-type Si—Ge mixed crystal 11 having alattice constant larger than silicon and epitaxially grown. The uppersurface of Si—Ge crystal epitaxially grown in the recess, which has adepth of about 50 nm, bulges above the silicon substrate surface. Thisbulged region applies compressive stress effectively to the channelregion under the gate electrode 5. A Ge composition of Si—Ge mixedcrystal is preferably 20 at % or smaller. Instead of Si—Ge, C-addedSi—Ge, Si—Ge—C, may be epitaxially grown. Although lattice mismatchbecomes smaller, stability is improved. If C is added, the Gecomposition is preferably 25% to 30%. Si—Ge crystal and Si—Ge—C crystalare collectively called Si—Ge-containing crystal in some cases.

As illustrated in FIG. 1K, the PMOS region is covered with a photoresistpattern PR3, and the SiN film 7 on the NMOS region is anisotropicallydry-etched by using CF₄ as etching gas. Since the silicon oxide film 8not covered with the silicon film of the side wall shape was removed byetching illustrated in FIGS. 1H and 1I, the silicon nitride 7 exposedoutside the silicon oxide film 8 is etched. The silicon nitride film 7covered with the silicon oxide film 8 is not etched, and is left in anL-shape together with the silicon oxide film 8.

Next, source/drain forming impurity ions are implanted into the NMOSregion deeper than the extensions Exn at a high concentration to formdeep and low resistivity source/drain regions S/Dn. For example, P ionsare implanted at an acceleration energy of 10 keV and a dose of 6×10¹⁵cm⁻² (6E15). The photoresist pattern PR3 is thereafter removed. Rapidthermal annealing (RTA) is performed, for example, for 2 seconds orshorter at 1000° C., to execute an activation process for activatingimplanted impurity ions in a short time.

As illustrated in FIG. 1L, a Ni layer is deposited on the wholesubstrate surface to a thickness of about 15 nm by sputtering. Annealingprocess is performed at a temperature of about 350° C., to cause asilicidation reaction. Unreacted Ni layer is removed, for example, byHNO₃ washing. A silicide layer 12 is left on the gate electrodes, on thesource/drain regions in the NMOS region, and on the Si—Ge epitaxiallayers 11 in the PMOS region. A thickness of the silicide layer 12 isabout 20 nm. Care is paid not to form nickel disilicide which has highresistance and is likely to be crystallized.

As illustrated in FIG. 1M, a silicon nitride film 14 having tensileintrinsic stress is deposited on the substrate to a thickness of 100 nmby plasma-enhanced CVD, for example, under the following conditions.SiH₄, NH₃ and N₂ are used as source gases, a growth temperature is 250°C. to 450° C., and an atmospheric pressure during growth is 2 Torr to 5Torr. Since the silicon nitride film 14 is formed on the side wallspacer with the L-shaped cross section formed by removing thesacrificial film, a distance from the silicon nitride film to thechannel becomes shorter. It is considered that stress can be appliedeffectively.

A photoresist pattern is formed covering the NMOS region, and thesilicon nitride film 14 having the tensile intrinsic stress in the PMOSregion is removed. The photoresist pattern covering the NMOS region isthereafter removed.

As illustrated in FIG. 1N, a silicon nitride film 15 having compressiveintrinsic stress is deposited on the substrate to a thickness of 100 nmby plasma-enhanced CVD, for example, under the following conditions.Organo silane, NH₃ and N₂ are used as source gases, a growth temperatureis 250° C. to 450° C., and an atmospheric pressure during growth is 2Torr to 5 Torr. Since the silicon nitride film 15 is formed on the sidewall spacer with the L-shaped cross section formed by removing thesacrificial film, a distance from the silicon nitride film to thechannel becomes shorter. It is considered that stress can be appliedeffectively.

A photoresist pattern is formed covering the PMOS region, and thesilicon nitride film 15 having the compressive intrinsic stress in theNMOS region is removed. The photoresist pattern covering the PMOS regionis thereafter removed.

In the manner described above, it is possible to cover the surface ofthe NMOS region with the etch stopper having tensile stress, to burySi—Ge epitaxial crystal having a lattice constant larger than silicon inthe recesses, and to cover the surface of the PMOS region with the etchstopper having compressive stress.

As illustrated in FIG. 1O, a silicon oxide film 17 is deposited on thesubstrate by plasma-enhanced CVD, and the surface thereof is planarizedby chemical mechanical polishing (CMP). A photoresist pattern havingopenings corresponding to contact holes is formed on the silicon oxidefilm 17. Contact holes are formed extending through the silicon oxidefilm 17 and reaching the etch stopper silicon nitride films 14 and 15 bydry etching using mixed gas of CF₄/N₂. By changing etching gas to CF₄,the silicon nitride films 14 and 15 are etched to complete the contactholes exposing the silicide layers. Ti/TiN or the like is sputtered toform barrier layers, and W layers are formed by CVD using WF₆/H₂ to buryconductive plugs 18 in the contact holes. Metal layers unnecessarilyformed on the silicon oxide film 17 are removed by CMP.

An insulating layer 19 such as silicon oxide is deposited by CVD,covering the conductive plugs 18. Wiring trenches are etched in theinsulating layer 19. A barrier layer of TaN or the like and a copperseed layer are deposited by sputtering on the substrate provided withthe wiring trenches, a copper layer is plated to fill the trench. Metallayers unnecessarily formed on the insulating layer 19 are removed byCMP to form copper wirings 20. Interlayer insulating films and IL2 areformed in which damascene copper wirings W1 and W2 are buried. Damascenewirings are formed by processes similar to the above-describedprocesses. The lowest interlayer insulating film includes a copperdiffusion preventive film of SiC, SiN, SiCN or the like. An organicinsulating resin such as SiLK (registered trademark), a porous silicafilm or the like may be used as the main interlayer insulating film.

In the first embodiment, a lamination of the insulating film and asacrificial film is formed to form the side wall spacers on the sidewalls of the gate electrode. In the PMOS region, the recesses are formedand the sacrificial film is etched and removed, in the same process. Itis possible to form the recesses and thin the side wall spacers. If dryetching is performed after the epitaxial growth to thin the side wallspacers, damages may be introduced into the epitaxial layer. Thesedemerits are avoided.

By forming the oxide film on the nitride film, the side wall spacers ofthe L-shape are formed also in the NMOS region so that the source/drainregions S/Dn are spaced from the gate electrode. If only PMOStransistors are formed, the silicon oxide film 8 on the silicon nitridefilm 7 may be omitted. A lamination of the insulating film andsacrificial film is formed, first the sacrificial film isanisotropically etched to form the side wall spacers, ion implantationfor forming envelope regions is performed, the sacrificial film isetched simultaneously with etching the recesses.

Although sacrificial film etching and recess etching are performed byisotropic chemical etching, etching is not limited thereto. For siliconetching for forming the recesses in the silicon substrate illustrated inFIG. 1H, a combination of anisotropic etching and isotropic etching maybe used. For example, first ordinary anisotropic dry etching isperformed under the conditions of etching gas of CF₄/O₂, a pressure of20 Pa, and a applicator power of 200 W, and thereafter, isotropic wetetching is performed with 10% diluted trimethylammoniumhydride (TMAH).Isotropic chemical etching may also be performed. Although residues areleft on the side walls of the gate electrode during anisotropic dryetching, it is possible to remove completely the residues by thesucceeding isotropic etching.

FIGS. 2A to 2D are cross sectional views of a semiconductor substrateillustrating main processes of a method for manufacturing asemiconductor device according to the second embodiment. The processesof isolation, well formation, gate electrode formation and extensionformation illustrated in FIGS. 1A to 1C of the first embodiment areexecuted first.

As illustrate in FIG. 2A, a lamination structure for forming side wallspacers is deposited on a silicon substrate, covering the gateelectrodes. A silicon oxide film 6 having a thickness of about 3 nm/asilicon nitride film 7 having a thickness of about 10 nm to 15 nm/and asilicon oxide film 8 having a thickness of about 6 nm are deposited byCVD at a temperature of about 500° C. to 600° C. Up to this process, theprocesses are similar to the first embodiment. Next, a silicon nitridefilm 29 is deposited to a thickness of about 10 nm to 15 nm at asubstrate temperature of 400° C. to 500° C., and at a power of 100 W to300 W, by plasma enhanced CVD (PE-CVD) using SiH₄/NH₃ as source gases.

As illustrated in FIG. 2B, the PE-CVD silicon nitride film 29 isanisotropically dry-etched using CF₄ as etching gas, to leave thesilicon nitride film only on the side walls of the gate electrodes in aside wall spacer shape.

As illustrated in FIG. 2C, in the state in which the silicon oxide film8, silicon nitride film 7 and silicon oxide film 6 are not etched yet,the NMOS region is covered with a resist pattern PR2. In the PMOSregion, by using the side wall spacers 29 of the silicon nitride film asan etching mask, the silicon oxide film 8, silicon nitride film 7 andsilicon oxide film 6 are anisotropically dry-etched to leave side wallspacers on the side walls of the gate electrode. The insulatinglamination on the upper surface of the gate electrode is also removed.Etching gas may be CF₄/N₂ for silicon oxide, and CF₄ for siliconnitride. In the PMOS region, the silicon substrate surface outside theside wall spacers is exposed.

B ions are implanted into the PMOS region to form deep p-type enveloperegions Evp. The p-type envelope region Evp is the region for covering ahetero interface to be later formed. The photoresist pattern PR2 isthereafter removed.

As illustrated in FIG. 2D, in the PMOS region, chemical dry etching isperformed for the silicon substrate which has the source/drain regionsexposed, by using CF₄/O₂ as etchant gas. For example, a pressure is 50Pa and an applicator power is 100 W. This chemical dry etching digs thesilicon surface exposed in the PMOS region to a depth of about 50 nm toform recesses 10 in which Si—Ge mixed crystal is to be epitaxiallygrown.

As compared with a silicon nitride film formed by thermal CVD, thesilicon nitride film 29 formed by PE-CVD lowers considerably an etchingselectivity with respect to silicon. This chemical dry etching not onlyetches the substrate silicon but also etches the PE-CVD silicon nitridefilm 29 on the side walls of the gate electrodes. The exposed siliconoxide film 8 in the NMOS region is also etched. The silicon oxide film 8under the silicon nitride film 29 is left in the L-shape. In the PMOSregion, the silicon oxide film 8 and underlying silicon nitride 7 areleft in the L-shape. The PE-CVD silicon nitride films 29 on the sidewalls are removed completely. In the NMOS region, the PE-CVD siliconnitride films 29 and exposed silicon oxide films are removed.

The side wall spacers of the PE-CVD silicon nitride films 29 areremoved, and the side wall spacers on the side walls of the gateelectrodes are thinned. The bottom wall of the three-layer laminationstructure projects in a lateral direction by a distance corresponding tothe thickness of the PE-CVD silicon nitride film 29. A projection lengthis approximately 7 nm or longer. The side walls of the gate electrodesretain the insulated state by the insulating lamination of the siliconoxide film 8, silicon nitride film 7 and silicon oxide film 6.

Thereafter, an HF process is executed slightly as a preparatory processfor epitaxial growth to remove a thin (natural) oxide film on thesilicon surface. Thereafter, processes corresponding to FIGS. 13 to 10of the first embodiment are executed to complete a semiconductor device.In the NMOS region, the silicon nitride film 7 covered with the siliconoxide film 8 is left in the L-shape to constitute thinned side wallspacers. An etch stopper containing stress is formed covering thethinned side wall spacers.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinventions have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

1. A method for manufacturing a semiconductor device comprising: (a)forming a gate insulating film and a gate electrode above a siliconsubstrate, (b) forming a first insulating film above the siliconsubstrate, covering said gate electrode, forming a sacrificial filmabove the first insulating film, and etching the sacrificial film andthe first insulating film to form side wall spacers on side walls of thegate electrode; (c) implanting an impurity into the silicon substrate onboth sides of the side wall spacers; (d) etching the silicon substrateto form recesses in the silicon substrate, etching the sacrificial filmincluded in the side wall spacers; (e) forming Si—Ge-containing crystalin the recesses; and (f) forming a second insulating film containingstress, covering the side wall spacers.
 2. The method for manufacturinga semiconductor device according to claim 1, wherein said step (d)etches said sacrificial film.
 3. The method for manufacturing asemiconductor device according to claim 1, wherein said insulating filmincludes a silicon nitride film.
 4. The method for manufacturing asemiconductor device according to claim 3, wherein said insulating filmincludes said silicon nitride film and a silicon oxide film formedthereon.
 5. The method for manufacturing a semiconductor deviceaccording to claim 4, further comprising: (g) executing a wet processusing HF between said steps (d) and (e) to remove an oxide film onsurfaces of said recesses, while leaving said silicon oxide film of saidside wall spacers.
 6. The method for manufacturing a semiconductordevice according to claim 1, wherein said sacrificial film is anamorphous Si film.
 7. The method for manufacturing a semiconductordevice according to claim 6, wherein said step (b) comprises a step offorming said amorphous Si film by CVD at a temperature not higher than500° C.
 8. The method for manufacturing a semiconductor device accordingto claim 1, wherein said sacrificial film is a silicon nitride film. 9.The method for manufacturing a semiconductor device according to claim8, wherein said step (b) comprises a step of forming said siliconnitride film by plasma-enhanced CVD at a temperature not higher than500° C.
 10. The method for manufacturing a semiconductor deviceaccording to claim 1, wherein said step (f) forms a silicon nitride filmhaving compressive stress by plasma-enhanced CVD.
 11. The method formanufacturing a semiconductor device according to claim 1, wherein saidstep (d) performs dry etching using mixed gas of CF₄ and O₂.
 12. Amethod for manufacturing a semiconductor device comprising: (a) forminga gate insulating film and a gate electrode above a silicon substrate;(b) forming an insulating film including a silicon nitride above saidsilicon substrate, forming a silicon oxide film covering said insulatingfilm, forming a sacrificial film of amorphous silicon or silicon nitridecovering the silicon oxide film, and etching the sacrificial film, thesilicon oxide film, and the insulating film to form side wall spacers onside walls of said gate electrode; (c) implanting an impurity into saidsilicon substrate on both sides of said side wall spacers; (d) etchingsaid silicon substrate to form recesses in said silicon substrate, andetching said sacrificial film included in said side wall spacers andstopping the etching at said silicon oxide film; (e) formingSi—Ge-containing crystal in said recesses; and (f) forming a siliconnitride film containing stress, covering said side wall spacers.
 13. Themethod for manufacturing a semiconductor device according to claim 12,wherein said step (b) forms said insulating film by stacking from alower side, a silicon oxide film, a silicon nitride film and a siliconoxide film.
 14. The method for manufacturing a semiconductor deviceaccording to claim 13, wherein said step (d) performs dry etching usingmixed gas of CF₄ and O₂.